Whales, Dolphins, and Porpoises of the Western North Atlantic Part 31

VENTRAL COLOR

White coloration of belly White coloration of belly extends high onto sides of extends to lower jaw but not body. above flippers on sides.

CAUDAL CRESTS

Tail stock strongly compressed Tail stock less laterally laterally; taller, narrows compressed, tapers more rapidly just in front of flukes. gently towards tail flukes.

[Ill.u.s.tration: Figure 138.--An Atlantic white-sided dolphin off the eastern Canadian coast. These animals do not usually ride the bow wave, but when they can be examined at close range, they can be readily distinguished from their more northerly cousins, the white-beaked dolphins, by their highly distinctive color pattern. (_Photo by P. B.

Beamish._)]

[Ill.u.s.tration: Figure 137.--Atlantic white-sided dolphins at sea between Cape Cod, Ma.s.s. and Nova Scotia. This species can be positively identified by the elongated zone of white and the adjacent region of tan or yellowish tan below and behind the dorsal fin, visible even in the fast-swimming animal in the bottom picture. The top photo ill.u.s.trates the origin of the Newfoundland common name "jumper." (_Photos by K. C.

Balcomb (top) and H. E. Winn (bottom)._)]

[Ill.u.s.tration: Figure 139.--The highly distinctive pattern of the Atlantic white-sided dolphins is clearly visible in this animal stranded in Scotland. Even if the color pattern has faded, however, this species should be easy to identify. The 30-40 teeth in each of the upper and lower jaws permit distinction from the white-beaked dolphins, which have only about 22-28 per side in each jaw. (_Photos by B. Tullock, courtesy of A. S. Clarke._)]

WHITE-BEAKED DOLPHIN (T)

_Lagenorhynchus albirostris_ Gray 1846

Other Common Names

White-beaked porpoise, squidhound (Newfoundland).

Description

White-beaked dolphins reach a maximum overall length of about 10 feet (3.1 m). The body is robust in form with a tall, uniformly dark-gray dorsal fin, and a short but distinct beak which, as the common name implies, is often light gray to white above and below, at least in European waters. The beak of animals in the western Atlantic populations is less frequently white. The back and sides are basically dark gray to black, and the belly is white to light gray.

Swimming white-beaked dolphins can be most readily identified by the two areas of pale coloration on the sides, one in front of and another below and behind the dorsal fin. These areas are clearly visible from a s.h.i.+p or aircraft as the animals roll at the surface.

Natural History Notes

White-beaked dolphins may sometimes occur in herds of up to 1,500 individuals. Like their cousins, the Atlantic white-sided dolphins, they do not commonly ride the bow waves of vessels.

White-beaked dolphins feed on squid, octopus, cod, herring, capelin, and sometimes on benthic crustaceans.

May Be Confused With

In their northerly range white-beaked dolphins are likely to be confused with only the Atlantic white-sided dolphins. The most distinctive features of white-beaked dolphins are 1) the two areas of paleness described above, 2) the prominent, dark gray dorsal fin, and sometimes 3) the white beak. Other features by which the two species may be distinguished in the brief encounters typical at sea are tabularized on p. 127.

Distribution

White-beaked dolphins are the more northerly of the two species of _Lagenorhynchus_ in the western North Atlantic. They are found from Cape Cod, Ma.s.s., north to western and southern Greenland and Davis Straits, though they are apparently far more numerous to the north of this range.

They appear in Davis Straits in spring and summer and leave that area in autumn, sometimes as late as November, to move southward. They winter as far south as Cape Cod, where they are the common dolphin species in April, May, and June (sometimes to July). Their migrations are poorly known.

Stranded Specimens

Stranded white-beaked dolphins can be most readily distinguished from white-sided dolphins by the substantial differences in coloration and the differences in numbers of teeth.

ATLANTIC WHITE-SIDED WHITE-BEAKED DOLPHIN DOLPHIN

TEETH

22-28 per side per jaw. 30-40 per side per jaw, sometimes more in upper jaw.

COLORATION

Beak sometimes gray or Beak all black; side marked white above and below; two with elongated areas of pale areas visible on living white with streaking patterns animals not visible on stranded of yellow and tan.

specimens.

Additional characteristics by which the two species may be distinguished are summarized on p. 123.

[Ill.u.s.tration: Figure 140.--Two views of white-beaked dolphins off Newfoundland. This species is characterized by a prominent uniform dark gray dorsal fin and two areas of paleness on the sides, one in front of and one below and behind the dorsal fin. White-beaked dolphins are distributed from Newfoundland north, extending to more northerly waters than Atlantic white-sided dolphins. (_Photos by H. E. Winn (bottom) and W. A. Watkins (top)._)]

[Ill.u.s.tration: Figure 141.--White-beaked dolphins reach nearly 10 feet (3.1 m) in length. Stranded animals, such as this specimen from Scotland, should be distinguishable from Atlantic white-sided dolphins by their differences in coloration. This species sometimes has a white beak and always lacks the elongated white patch and tan or yellow streaking found on the side of Atlantic white-sided dolphins. (_Photos by A. S. Clarke._)]

ATLANTIC BOTTLENOSED DOLPHIN (T)

_Tursiops truncatus_ (Montague 1821)

Other Common Names

Bottlenosed porpoise, gray porpoise, common porpoise.[12]

[Footnote 12: See also p. 150 for use of this common name for another species, the harbor porpoise.]

Description

Atlantic bottlenosed dolphins reach a maximum overall length of about 12 feet (3.7 m) and weigh in excess of 1,430 pounds (650 kg). They have relatively stubby snouts and dorsal fins, which are broad at the base, tall, and falcate. Coloration varies slightly, but individuals are usually dark gray on the back, lighter gray on the side, grading to white or pink on the belly. Old females may have spots on the belly. The dark coloration of the back often appears as a highly distinct cape, particularly on the head.

Natural History Notes

Atlantic bottlenosed dolphins often occur in groups of up to several hundred individuals which usually consist of aggregations of small groups of no more than a dozen animals each. They frequently a.s.sociate with the Atlantic pilot whales and are frequently found accompanying the right and humpback whales travelling along the Atlantic coast of Florida.

Atlantic bottlenosed dolphins have catholic tastes, feeding on shrimp, eels, catfish, menhadden mullet, and miscellaneous trash fish, to mention only a few. They are frequently found near shrimp boats, feeding on fish stirred up by the trawls or on discarded trash fish.